Plastisols containing glycerol esters as plasticizers

ABSTRACT

Plastisols and organosols are provided that include plasticizers that include mono-, di- and triesters of glycerol. The plasticizers are good solvators for polyvinyl chloride and impart low plastisol and organosol viscosities.

The present invention relates to plastisol compositions that includeglycerol esters which are effective plasticizers for plastisols oforganic polymers. In addition to compatibility with the organicpolymers, the glycerol esters exhibited unexpectedly good solvationcharacteristics. The plastisols described herein had low plastisolviscosities, low fusion temperature and increased gel strength.

BACKGROUND

Known prior art plasticizers for polymers include but are not limited toesters that are reaction products of 1) aliphatic or aromatic mono- anddicarboxylic acids with 2) mono- and dihydric alcohols or glycols.Typical plasticizers for vinyl chloride polymers include esters ofbenzoic acid with monomeric or oligomeric glycols and esters of phthalicacid with monohydric alcohols.

U.S. Pat. Nos. 6,652,774; 6,740,254; and 6,811,722, describe mixedesters of glycerol as phthalate-free plasticizers for resinous polymers,including vinyl polymers, rubbers, polyurethanes and acrylics. At leastone of the esters in the mixture exhibits the general formulaCH₂(OOR¹)CH(OOR²)CH₂(OOR₃) wherein at least two of R¹, R² and R³ aredifferent alkyl groups. In preferred embodiments R¹, R² and R³ containup to 11 carbon atoms each, preferably from 2 to about 11 carbons each.

The ester compositions described in the aforementioned patents aremixtures prepared by reacting a mixture of at least two carboxylic acidswith glycerol. The types and relative concentrations of the individualesters in the resultant mixtures vary from batch to batch. Thisvariation makes it difficult to predict the composition of a particularbatch or the level of plasticization that would be imparted to a polymerby that batch and, more importantly, the concentration of a particularbatch of plasticizer required to achieve a desired degree ofplasticization.

U.S. Pat. No. 5,444,110, describes crosslinkable plastisols wherein thepolyvinyl chloride resin contains epoxy groups. The specification ofthis patent contains a listing of over 100 esters commonly used asplasticizers.

SUMMARY

Environmentally friendly plasticizers for plastisols are provided. Theplasticizers impart a predictable degree of plasticization to aplastisol or organosol, making it possible to calculate and include thequantity of plasticizer required to achieve a desired level ofplasticization in a plastisol or organosol based on rigid polymers suchas vinyl chloride and copolymers thereof.

In one aspect, polymer composition are provided that include athermoplastic polymer selected from the group consisting of homopolymersand copolymers of vinyl chloride, and homopolymers and copolymers ofacrylic; and an amount of plasticizer effective for plasticizing thethermoplastic composition. The plasticizer includes a glycerol esterselected from the group consisting of mono-, di- and triesters ofglycerol and mixtures thereof. Glycerol esters which can be utilizedhave a general formula

-   wherein 0 to 2 X groups are hydroxyl and 1 to 3 X groups are

-   wherein R¹ is —(CH₂)_(n)—CH₃, where n is 0 to 5,-   wherein all R¹ groups are identical,-   and wherein if n is 0, then 1 to 2 X groups are hydroxyl.

Shaped articles are provided that are selected from the group consistingof films, coatings, molded articles, extruded articles, cast articles.The shaped articles are formed from polymer compositions describedherein.

A method is provided for making a polymer composition. The methodincludes dispersing organic polymer and blending a glycerol ester of thegeneral formula with the polymer in an amount effective for plasticizingthe polymer.

DETAILED DESCRIPTION

The present plasticizers are compatible with a variety of polymerstypically used in the formulation of plastisols. These polymers includebut are not limited to vinyl chloride homopolymers and copolymers, andacrylic homopolymers and copolymers. Plastisols are blends ofplasticizers with PVC. In addition plastisols will generally containheat stabilizers and other ingredients such but not limited to fillers,pigments, solvents, UV stabilizers, antioxidants, dispersants, blowingagents such as but not limited to azodicarbonamide, kickers for theblowing agent(s) and other adjuvants to tailor the composition to theapplication. As used herein, plastisols include acrylic homopolymers andcopolymers as these newer resins were designed to replace PVC in“plastisol or organosol” compositions. The acrylic compositions may alsoinclude at least some of the additional materials described herein.

Glycerol tributyrate has been found to be compatible to at least 40% ofa plastisol composition based on homopolymer polyvinyl chloride.Compatibility of a given ester with a polymer can be determined byblending the desired amount of glycerol ester with a finely divided formof the polymer at a temperature of 25° C., fusing the plastisolcomposition and determining the compatibility of the plasticizer with aplastic sheet thus prepared.

The glycerol esters of this invention can be the only plasticizer in theplastisol or organosol. Alternatively, these esters can be used incombination with other plasticizers conventionally used with theselected polymer. In the case of vinyl chloride polymers theseadditional plasticizers include but are not limited to esters derivedfrom a) the reaction of monofunctional alcohols with monofunctionalacids aliphatic of aromatic monocarboxylic acids; b) the reaction ofglycols or diols with monofunctional acids such as benzoic acid, or c)the reaction of an alkyl or aromatic dicarboxylic acid such as phthalicacid with a monofunctional or polyfunctional alcohol. Esters of benzoicacid together with mono- and diesters of the isomericcyclohexanedicarboxylic acids, also referred to as hexahydrophthalicacids, are preferred classes of auxiliary plasticizers. Otherplasticizers that can be used include but are not limited to compatiblemembers of the following families: citrates, sulphonamides, alkylsulfonic acid esters, adipates, saturated low molecular weightpolyesters, isobutyrates and glutarates.

Many of the glycerol esters suitable as plasticizers in the presentpolymer compositions are commercially available. Those which are not canbe prepared using known esterification reactions involving glycerol anda monocarboxylic acid containing from 3 to 6 carbon atoms. The molarratio of acid to glycerol will be substantially equivalent to theaverage number of esterifies hydroxyl groups per molecule desired in thefinal ester. In the case of the tributyl ester, this product iscommercially available as n-butyl ester, isobutyl ester or mixturesthereof.

Any objectionable odor of higher glycerol esters such as the tributyratein a plastisol or organosol may be masked using small quantities offragrances including but not limited to juniper oil. At higher hydroxylcontent the odor of the ester is significantly reduced.

Plastisols and organosols containing the plasticizers of this inventioncan be prepared using conventional techniques for preparing thesecompositions. In accordance with one method, the glycerol ester or amixture of these esters together with any desired additionalplasticizers are blended with a finely divided form of the polymer to bemodified.

The present plasticizers will wet and slowly solvate particles of afinely divided resinous polymer such as a vinyl chloride homo- orcopolymer. Mixtures of finely divided polymer and plasticizer can bemolded into shaped articles using slush molding or other conventionaltechniques, cast to form films or coatings on a variety of substrates,dip coated onto an existing shaped articles such as gloves or coated onto a substrate such as sheets of flooring material formed from a vinylor other type of polymer. Gelation of the polymer typically occurs attemperatures below 150° C. The resin particles are then fused by heatingthe initial film or other shaped article to between about 150 and 210°C. for a sufficient time to develop maximum physical properties.

Plastisols prepared using the plasticizers described herein arecharacterized by excellent Theological properties at both low and highshear rates. This property is particularly advantageous, in for example,the preparation of vinyl flooring, during which a vinyl sheet is coatedwith the plastisol, following which the plastisol is then allowed togel. The resultant coated sheet is then rolled up prior to final fusingof the polymer.

Plastisols and organosols containing one or more of the glycerol estersdescribed herein in combination with polymers, such as the homopolymersand copolymers of vinyl chloride and other polymers described, aresuitable for use alone or in combination with known plasticizers in avariety of additional end use applications. End use applications mayinclude but are not limited to films, coatings, the fabrication ofshaped articles by known techniques, including but not limited to slush,dip, rotational molding, and casting.

Organic liquids suitable for use in organosols include but are notlimited to aliphatic, cycloaliphatic, aromatic, and mixed solvents atlevels to assist in the control of rheology and therefore applicationproperties.

Organosols are used in some applications where viscosity control can notbe achieved by the selection of plasticizer or level of plasticizerrequired is not adequate. For example, highly filled plastisolssometimes require solvent use to achieve proper application rheology.The plasticizers of this invention can be used to advantage to controlviscosity and rheology with less or no solvents thus eliminating orreducing volatility issues.

An environmentally important advantage of the present esters is thatthey can be prepared using glycerol and acids obtained from naturallyoccurring materials in contrast to the petroleum-based reactants used toprepare conventional plasticizers based on aromatic mono- anddicarboxylic acids.

The use of the glycerol esters of the present invention provides adecrease in viscosity of the plastisol composition of about 70% to about80% after 1 hour and a decrease in viscosity of the plastisolcomposition of about 70% to about 80% after 1 day, as compared toplastisol compositions made with DOP (di-2-ethylhexyl phthalate) or DINP(diisononyl phthalate) as the plasticizer.

The following examples describe preferred polymer compositions andplasticizers of the present invention. The examples should not beinterpreted as limiting the scope of the present invention as describedin the accompanying claims. Unless otherwise specified all parts andpercentages are by weight.

EXAMPLES

Plastisol compositions were prepared by blending 100 parts of a finelydivided vinyl chloride homopolymer available as Geon 121A from Polyone,3 parts of a calcium/zinc based heat stabilizer available as Mark 1221from Chemtura with one of the following glycerol eaters: 1) 70 parts ofglycerol tributyrate (low hydroxyl content), 2) 70 parts of glyceroltrioctoate. As controls for the evaluation diisononyl phthalate (DINP)and di-2-ethylhexyl phthalate (DOP) were also evaluated. The resultantmixtures were blended as described in the following detailed procedureto form plastisols.

A homogeneous blend of 100 parts of the polymer and 70 parts of glyceroltrioctoate could not be prepared due to the incompatibility of thisamount of ester with the polymer. This composition therefore could notbe evaluated using some of the test procedures used for the other twoplastisol samples.

Plastisol Preparation

Equipment

-   -   Vessel: A 19 ounce-capacity unlined steel can suspended in water        bath    -   Mixing Device: High torque overhead stirrer equipped with 2″        high speed dispersion blade set approximately ½″ above bottom of        can        Preparation    -   1. The plasticizer were placed in the can    -   2. Started timer and began mixing @ 700 rpm    -   3. Mixed for 1 minute    -   4. Added polyvinyl chloride and heat stabilizer    -   5. Increased speed to 1250 rpm    -   6. Stopped mixing after 12 minutes    -   7. Degassed sample for 20 minutes under vacuum and agitation        Plastisol Sheet Fusion        Equipment    -   Two 10″×9″×⅛″ clean glass sheets    -   Four 1″×1″×0.048″ glass shims        Preparation    -   1. Placed one glass sheet on a flat and level bench top    -   2. Placed a glass shim at each corner of this sheet    -   3. Poured a pool of plastisol in the middle of the glass sheet    -   4. Placed the second glass sheet on top of the first in a manner        that did not trap any air in the plastisol pool    -   5 Pressed down on each shim to insure uniform plastisol        thickness    -   6. Placed the mold assembly into a forced air oven for 10        minutes @ 190° C.    -   7. Removed mold assembly and separated the fused sheet from the        glass and allow to cool        Test Methods        Viscosity:

Measured using TA model AR-2000 rheometer under the following conditions

-   -   Method type: Flow    -   Geometry: 2 cm steel plate on peltier plate with 500 micron gap    -   Temperature: 25° C.    -   Test Method: Pre-shear 66.30 Pa for 10 sec        -   Equilibrate (no shear) for 30 sec        -   Shear ramp 2-900 1/s over 90 sec    -   Report: Viscosity at 100 and 500 sec⁻¹

Brookfield viscosity: Measured using ASTM D1824 -95 at 20 RPM.

Gel/Fusion:

Measured using TA model AR-2000 rheometer under the following conditions

-   -   Method type: Oscillation    -   Geometry: 2 cm steel plate with 500 micron gap    -   Temperature: 40 to 210C at a rate of 5° C./minute    -   Test Method: Initial stress of 0.2 Pa for 10 sec    -   Frequency: 1 Hertz    -   Displacement: 0.0001 radians    -   Report: Temperature at G′=500 Pa (gel temperature value); G′        peak temperature and stress; G′ X G″ cross is indication of        final fusion.

-   Tensile Properties: ASTM D 638-03, Type IV specimen,    -   Speed of tester was 20 in/min

-   Durometer Hardness Measured using ASTM test method 2240-97, Shore A

-   Loop Spew: 1″×3″ samples were cut from the fused sheets. An “X” was    made with a ball point pen in the center of the sample. The sample    was bent to form a loop with the “X” on the inside surface of the    loop. The loop was clipped with a binder clip with the inside center    of the loop at a distance of ¼″ from the grip of the clip.    -   The loop was maintained for the specified time periods at a        temperature of 23° C. At the end of the test interval the loop        was removed from the clip and the loop folded in the opposite        direction. The inner surface of the loop, which had maximum        stress, and therefore maximum likelihood of exudation, was        examined for exudation of plasticizer. Samples were rated        according to the following scale:        -   0—no exudation,        -   1—Slight exudation; “X” smears or trace of exudate;        -   2—Moderate—small spots of exudate,        -   3—Heavy—area totally wetted.

-   Roll spew: 1″×3″ samples were cut from the fused sheets, covered    with 1″×3″ pieces of yellow paper, rolled and secured roll with a    rubber band. The samples were then placed in a 60° C. forced air    oven for 1 day, following which they were removed and allowed to    cool. Each sample was then unrolled and any exudation of liquid    evaluated according to the following scale: 0—no stain on paper,    1—slight stain on paper, 2—definite stain, oil layer on film,    3—severe stain, oily film

-   Carbon Volatility: Evaluated using ASTM test procedure D1203-94    Method A

TEST RESULTS

TABLE 1 Plastisol Viscosity and Rheology Test DOP DINP TributyrateTrioctanoate Brookfield RVT, mPa · s 1 hr. 1850 1780 430 480 1 day 24002150 640 508 AR 2000, Initial, Poise 100 sec −1 3.09 3.8 0.52 1.73 500sec −1 5.65 8.27 0.91 3.88

TABLE 2 Plastisol Gel/Fusion Data Test DOP DINP Tributyrin TrioctanoateG′ Inflection, @ 76 83 62 125 500 Pa G′ Pa 278,900 263,800 409,00060,000 Temperature, ° C. 123 132 106 152 G′ X G″ upper 187.5 189 190 196intersection, temperature, ° C.

TABLE 3 Physical Performance Data Tests DOP DINP TributyrateTrioctanoate* Compatibility Com- Com- Compatible Incompatible patiblepatible Loop rating, 4 0 0 0 NA weeks Roll rating, sum 0 0 0 NA of 3days Tensile Data Tensile at Break, 2323 2310 2136 NA psi 100% Modulus,779 857 624 NA psi Elongation, % 475 440 500 NA Shore A, 10 sec. 57 5854 NA Activated Charcoal 1.5 1.4 8.3 NA volatility, % lost, 24 hours,70° C. *= Glycerol trioctoate at a concentration of 70 phr wasincompatible with the polymer and was not tested further.

The data above demonstrates that glycerol tributyrate is compatible, agood solvator (as indicated by G′ peak temperature, G′ level and G′inflection) for PVC (much better than DOP or DINP) and, surprisingly,plastisols based on the glycerol tributyrate have low viscosities andgood rheology as indicated in the comparison to plastisols based ondiisononyl phthalate (DINP) or di-2-ethylhexyl phthalate. Glyceroltributyrate is an efficient plasticizer but is volatile compared to thegeneral purpose plasticizers. While it is relatively volatile, it can bea very useful plasticizer for viscosity control of plastisols and otherapplications.

1. A polymer composition comprising: a) a thermoplastic polymer selectedfrom the group consisting of homopolymers and copolymers of vinylchloride, and homopolymers and copolymers of acrylic; and b) an amountof plasticizer effective for plasticizing the thermoplastic polymer, theplasticizer including least one ester selected from the group consistingof mono-, di- and triesters of glycerol corresponding to the generalformula

wherein 0 to 2 X groups are hydroxyl and 1 to 3 X groups are

wherein R¹ is —(CH₂)_(n)—CH₃, where n is 0 to 5, wherein all R¹ groupsare identical, and wherein if n is 0, then 1 to 2 X groups are hydroxyl.2. The polymer composition according to claim 1 wherein R¹ includes from3 to 6 carbon atoms.
 3. The polymer composition according to claim 1wherein the polymer composition includes from about 1 to about 70 partsby weight glycerol ester per 100 parts thermoplastic polymer.
 4. Thepolymer composition according to claim 1 wherein the composition has aratio of glycerol to carboxylic acid of about 1 to 2.5 to about 1 to3.0.
 5. The polymer composition according to claim 1 wherein theplasticizer is glycerol tributyrate.
 6. The polymer compositionaccording to claim 1 wherein said composition contains at least oneadditional plasticizer selected from the group consisting of a) thereaction products of monofunctional alcohols with monofuctional acidsaliphatic of aromatic monocarboxylic acids; b) the reaction of glycolsor diols with monofunctional acids such as benzoic acid, and c) thereaction of at least one carboxylic acid selected from the groupconsisting of alkyl and aromatic dicarboxylic acids with at least onealcohol selected from the group consisting of monofunctional andpolyfunctional alcohols and monomeric and oligomeric glycols.
 7. Thepolymer composition of claim 1 wherein said composition contains atleast one additional plasticizer selected from the group consisting ofphthalates, terephthalates, citrates, sulphonamides, alkyl sulfonic acidesters, adipates, saturated low molecular weight polyesters,isobutyrates, and glutarates.
 8. The polymer composition of claim 1wherein the glycerol ester is a blend of from 1 to 70 parts by weightper 100 parts of said thermoplastic polymer of a first ester and fromabout 30 to about 100 parts by weight per 100 parts of saidthermoplastic polymer of a second ester.